PREFACE 



The Text-book, as originally planned, is an outgrowth of the course in 

 Embryology given at the Medical Department of Columbia University. It was 

 intended primarily to present to the student of medicine the most important 

 facts of development, at the same time emphasizing those features which 

 bear directly upon other branches of medicine. As the work took form, it 

 seemed best to broaden its scope and make it of greater value to the general 

 student of embryology and allied sciences. With the opinion that illustrations 

 convey a much clearer conception of structural features than verbal description 

 alone, the writers have made free use of figures. 



The plan of adding brief "Practical Suggestions" at the end of each chapter 

 has been so thoroughly satisfactory in the Text-book of Histology, especially 

 in connection with laboratory work, that it has been adopted here. These 

 "suggestions" are not intended to be complete descriptions of embryological 

 technic, but are for the purpose of furnishing the laboratory worker with cer- 

 tain of the more essential practical hints for studying the structures described 

 in the chapter. To avoid frequent repetition, some of the best methods of 

 procuring, handling, and preparing embryological material, and some of the 

 more important formulae are given in the Appendix, which is intended to be 

 used mainly for the carrying out of the "Practical Suggestions." 



The development of the Germ Layers has been treated rather elaborately 

 from a comparative standpoint, because this has been found the most satisfac- 

 tory method of teaching the subject. 



In the chapter on the Nervous System the aim has been to give a general 

 conception of the subject, which, if once mastered by the student, will give 

 him an insight into the structure and significance of the nervous system that 

 will bring this difficult subject more fully within his grasp. 



In Part II (Organogenesis), at the end of each chapter there is given a brief 

 description of certain developmental anomalies which may occur in connection 



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